Insulin C-peptide |
| Definition: |
| A blood test that measures the amount of C-peptide, a subunit of the hormone insulin. |
| Alternative Names: |
| C-peptide |
| How the test is performed: |
| Adult or child: Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. After the blood is collected, the tourniquet is removed to restore circulation. Then, the needle is removed, and the puncture site is covered to stop any bleeding. Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test: |
The preparation for the test depends on the reason for the c-peptide measurement. Ask your health care provider if you should fast prior to the test. The health care provider may advise you to withhold medications that can interfere with test results. Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
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C-peptide is measured to differentiate endogenous (produced by the body) from exogenous (injected into the body) insulin production. When insulin is initially synthesized by the beta cells of the pancreas, it is produced as a large molecule (propeptide). This molecule is then cleaved at 2. The intermediate segment (C-peptide) is released at the same time insulin is released but has no known function. The C-peptide level may be measured in a patient with type II diabetes mellitus to see if any insulin is still being produced endogenously. It may also be measured in the evaluation of hypoglycemia (low blood sugar) to see if too much insulin is being produced by the patient. |
| Normal Values: |
| 0.5 to 2.0 ng/ml Note: ng/ml = nanograms per milliliter |
| What abnormal results mean: |
| Normal values in a patient requiring insulin injections indicates that the person's body is still producing some insulin. Normal values in a patient who has low blood sugar indicates that the patient is making too much insulin. Low values (or no Insulin C-peptide) indicates that the person's pancreas is producing little or no insulin. |
| What the risks are: |
| Special considerations: |
| Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
Reviewed By: Stephanie Fish, M.D., Division of Endocrinology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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